Reusability in blockchain focuses on reusing pre-built components, such as smart contracts, algorithms, and protocols, across multiple dApps. This reduces development time, cuts costs, and enhances system efficiency. The chapter introduces Smart Contract as a Service (SCaaS), which provides reusable smart contract templates to developers. Reusability aligns with blockchain sustainability by lowering energy consumption and promoting long-term system scalability. By understanding the characteristics of reusable software components, blockchain developers can design and deploy flexible, interoperable, and secure systems, ultimately accelerating blockchain innovation.